This invention relates to an image processing system for use in combination with a recording medium, such as a compact disk read-only memory (abbreviated to a CD-ROM) to record and/or reproduce a sequence of image signals.
Recent attempts have been directed to a system for recording and reproducing a sequence of image signals on a CD-ROM which has been used only for recording and reproducing an audio signal.
According to the standard of the CD-ROM, such a CD-ROM should have a maximum readout rate of 150 kilobytes and a memory capacity of 540 megabytes. As long as the CD-ROM complies with this standard, a single frame of image signals should be coded into a coded signal of 5 kilobytes on condition that thirty frames of image signals appear for one second. Therefore, efficient coding or redundancy reduction coding is indispenable for recording or reproducing the image signals. Otherwise, it is impossible to reproduce a sequence of moving images from the CD-ROM. Herein, efficient coding may simply be called information reduction.
If information reduction is possible such that a single frame of the image signals is coded into a coded signal of 5 kilobytes, a long play reproduction of about one hour can be achieved as regards the image signals by the use of the CD-ROM.
In reality, a proposal for a color image recording CD-ROM has been offered which realizes as long a reproduction time as about one hour with a usual audio signal recording CD-ROM. In this case, the image signals are recorded on the color image recording CD-ROM in the form of a sequence of predictive error signals which appear as results of efficient coding and which may be referred to as a sequence of compressed image signals. The predictive coding may be carried out in a manner known in the field of data transmission. Such efficient coding may be, for example, interframe coding which is carried out with reference to both a present image signal and a past image signal and which is useful to favorably reduce the amount of significant information when coding a sequence of image signals.
In the meanwhile, it may be preferable for the CD-ROM to be able to perform not only normal reproduction but also a wide variety of other functions, such as a reverse reproduction, a high speed reproduction, scene skipping, an arbitrary reproduction from an arbitrary scene, as well as a video tape. However, it is difficult to perform the above-exemplified functions as long as the image signals are subjected to the interfame coding alone. More particularly, let us consider the image signals to be divided into a frame sequence from a first or leading frame to an end or trailing frame as leading through trailing compressed image signals are subjected to the interframe coding, respectively, and that the signals are successively recorded on the CD-ROM from the leading compressed image signal to the trailing compressed image signal in a normal order. Herein, the first through the end frames may be considered to correspond to first through end scenes, respectively, for convenience of description.
Now, under these circumstances, suppose that it is attempted to reproduce the image signals from the CD-ROM in a reverse order, starting from the end scene in response to a request issued from an operator or user to indicate the reverse reproduction. In this event, a nonsignificant or meaningless image is reproduced from the CD-ROM, irrespective of the images that were desired to be reproduced from the image signals. This is because no past image signals exist when reproducing the trailing compressed image signal is attempted. Likewise, it is also difficult to carry out such a reverse reproduction from an intermediate scene between the first and the end scenes.
This is also true of the high speed reproduction, the scene skipping, and the arbitrary reproduction from an arbitrary scene.
Nonsignificant reproduction of images may also be carried out when scenes are changed from one to another on recording compressed image signals as mentioned above.